Potential Evapotranspiration in the Southern Alberta Chinook Region

Several methods and equations exist in the literature for predicting potential evapotranspiration (PE), but the use of most of these equations is limited by the amount of climatic input data they require. The Jense-Haise equation requires only mean air temperature and solar radiation data but it appears to yield low estimates for the southern Alberta chinook region where the prevailing weather factor is wind. An empirical method was developed to modify the Jensen-Haise equation to account for the wind variable. The PE estimations obtained by the modified Jensen-Haise equation were evaluated by some widely known methods. An average of 20% improvement in seasonal PE was obtained. The modified equation was used as a driving function to estimate evapotranspiration and soil moisture for wheat, barley, and canola crops grown in 1987. The statistical analyses conducted on the measured and calculated soil moisture data indicated that soil moistures computed with the modified equation were not significantly different from those obtained with the gravimetric technique. This study confirmed that wind is a major factor in PE estimate in the southern Alberta region and showed that incorporating the wind parameter in the Jensen-Haise equation significantly improved the PE estimates for this region.